1. Field of the Invention
The invention relates to electrical energy management systems, and more specifically, to residential electrical energy management systems which shed and restore electrical controlled loads in accordance with priorities associated with the controlled loads to keep the total power consumption of a residence at a level which is less than but as near as possible to a selected power demand limit.
2. Description of the Prior Art
With the advent of higher fuel prices and increased capital costs, electrical utility companies have sought (and in some cases have been required by governmental regulation) to seek means for reducing the overall cost to the customer of electrical energy provided by the utility company.
Various energy management systems have been proposed which require or attempt to persuade utility company customers to limit their electrical energy consumption as a means of reducing their overall utility bills. According to one such proposal, the maximum load which each customer is allowed to place on the utility's power generation facilities is arbitrarily limited. Although this "peak usage curtailment" approach is partially effective in reducing the customer's overall utility bills, it has several decided disadvantages. The customer, especially a residential user, loses a degree of flexibility in selecting and using various electrical appliances, etc. in his residence and to this extent, the peak usage curtailment program has direct and often undesirable impact on the customer's lifestyle. The utility company itself may find that the reduction in total electrical energy consumption reduces the utility company's revenue to the point that it must, in turn, raise the charge per unit of electrical power consumed to the point that the user's electrical utility bills may even exceed the bills he customarily received before his power usage was curtailed.
It would be highly advantageous to provide an electrical energy management system which is particularly adapted for use in peak load curtailment programs as applied to residential customers which would allow arbitrary peak load limits to be imposed upon the customers with the minimum possible effect on the customer's lifestyle while simultaneously maintaining the total usage of power by the customer at or just below the predetermined permissible peak demand, thereby assuring the utility company of the optimum use of its generating facilities.
Accordingly, a principal object of the present invention is to provide an improved energy management system for use in connection with peak usage curtailment programs.
Another object of the invention is to provide an energy management system for use in conjunction with a peak usage curtailment program which energy management system is especially adapted for use by residential customers.
Still another object of the invention is to provide a residential energy management system which applies an arbitrary peak demand limit while retaining maximum flexibility of use of various residential appliances and maintaining power consumption consistent with the peak usage curtailment program.
Load-shedding devices which limit power consumption in residences, places of business and manufacturing plants are well known in the art. Such load-shedding devices usually consist of a sensor for measuring the total energy consumption of a residence or the like and means, such as relays, for shedding loads in a predetermined sequence when the demand exceeds the predetermined peak demand. Restoration of the loads may be automatic or manual but, until now, no energy management system has been devised which will automatically restore a load out of sequence if the restoration of that load can be accomplished without exceeding the imposed peak demand limit. Thus, while the prior art load-shedding and restoring systems do have the effect of reducing the peak load on the utility and shifting some of the energy usage to the former "off-peak" hours, the prior art systems also have the effect of significantly reducing the total power usage by the customer. Since the capital investment of the utility company must be amortized, without reference to the amount of power consumed, the utility is then forced to raise its unit price for power charged to the consumer. This cost increase may be so high that the customer's utility bill is actually increased, rather than decreased.
The state of the art for load shedding/restoring devices is believed to be indicated by U.S. Pat. Nos. 4,146,923; 4,075,699; 4,065,485; 3,652,838; 4,168,491; 4,059,747; 3,906,242; 4,023,043; 4,181,950; and 3,652,838.
Although the above references disclose a variety of complex systems and schemes for shedding loads in accordance with priorities associated therewith, none of the references disclose any systems or schemes for restoring the loads in a manner which results in maximum possible utilization of the various loads while nevertheless maintaining the power consumption of the residence below the power demand limit selected by the residence owner.
It therefore is another object of the invention to provide a power demand controller system which maximizes the power usage of an establishment while nevertheless maintaining the power usage below a preselected power demand limit.